Question: I'm trying to load an external script (let's say from example.com) in the Electron app. The External script loads everything in an iframe and it's using inline styles, which renders the widget without any styles due to Electron CSP. I don't want to use unsafe-inline CSP on the whole application, I need it just on this iframe which comes from "example.com".
Error which I get: Refused to apply inline style because it violates the following Content Security Policy directive: "default-src 'self'"
For resolving this I am thinking to add this code block in my electron app -
session.defaultSession.webRequest.onHeadersReceived((details, callback) => {
if(details.url.includes("example.com") && details.url.includes(".html")) {
callback({
responseHeaders: Object.assign({
"Content-Security-Policy": [ "default-src 'self';style-src 'unsafe-inline' https://*.example.com https://example.com" ]
}, details.responseHeaders)});
}
This code block will ensure to have 'unsafe-inline' CSP only in the iframes of "abc.com". But, I want to check that can this code block still cause any kind of security threat to my app?
Does your iframe contain any user entered data? If not then this is fine. If it does then you will need to find another way to check they have not entered any inline styles
Related
I am currently making a Content Security Policy (CSP) for a production application made with Next.js. While I have found trustworthy documentation for implementing a CSP with the framework, there are a couple of concerns that I want to make sure are addressed correctly.
Issue #1: I have read that security policies set in HTTP headers are preferable. However, I cannot find a way to pass a 'nonce' attribute for inline styles in production using this approach. https://nextjs.org/docs/advanced-features/security-headers
Issue #2: I've seen other examples where developers inject their CSP in the custom document("./pages/_document.js"). I am hesitant to use this approach because I hear meta-tag CSPs are easily bypassable. https://github.com/vercel/next.js/tree/canary/examples/with-strict-csp
My Questions:
Is there a way to use a 'nonce' with header configuration in "next.config.js"? If so, how?
Is specifying "unsafe-inline" for styles in production a security issue at all if Next.js automatically sanitizes user input? I should also mention that I sanitize all mongo database queries in my APIs as well.
Is there something about the meta tag approach described in Issue #2 that makes it as secure as the HTTP header approach?
What approach do you recommend I take to make my CSP as strong as possible for my web app?
All the best,
-Sam
NextJS has 2 pre-rendering mode: Static Site Generation(SSG) and Server-Side Rendering(SSR). The first one has no way to update nonce='value' in the HTML code, but when SSG you can pass a 'nonce' attribute for inline styles and scripts using ./pages/_document.tsx.
See an example for CSP header and meta tag CSP example.
Re Quersions:
I think using a next.config.js is possible, for example next-safe package adds a nextSafe() function into this file to set a lot of headers:
.
const nextSafe = require('next-safe')
const isDev = process.env.NODE_ENV !== 'production'
module.exports = {
async headers () {
return [
{
source: '/:path*',
headers: nextSafe({ isDev }),
},
]
},
}
To set 'nonce' into CSP header you can craft your own function in this way. To set 'nonce' attribute into styles you can use _document.tsx renderer.
Specifying 'unsafe-inline' for styles in production is not a security issue. For example https://accounts.google.com page allows inline styles (it even does not have style-src/default-src directives but it carefully controls scripts).
Setting CSP in HTTP headers is preferable but this does not mean that CSP in meta tag is easily bypassable. Just CSP in meta tag has some restrictions and if you do not use features that have been restricted you can safely use meta tag to delivery CSP.
You can strengthen the protection indefinitely, spending a lot of time and resources. Just follow the main principle "protection should not be more expensive than the protected object".
I want to define a content security policy that allows loading images from any origin by default but restricts this to allow only a specific set of origins in some sections of the website.
In a traditional website that makes a new HTTP request for every navigation, this could be easily done by sending a different Content-Security-Policy HTTP header for the pages that require the stricter policy. But in a single page application, this is of course not possible because navigating to a more restrictive section of the app does not cause a new HTTP request (also I would like to define policies on more dynamic conditions than a URL navigation).
I know that—besides in an HTTP header—CSP policies can also be defined in a meta tag and when multiple CSP policies are defined a request must pass all of them to be permitted. So my first approach to solving the problem was setting a default CSP in a Content-Security-Policy header for the entire page and then dynamically set more restrictive policies by adding a <meta http-equiv="Content-Security-Policy" content="…"> tag to the document's head when required.
And this works just fine for dynamically adding more restrictive policies. The big problem is that removing that meta tag or modifying it does not remove or modify the associated content security policy (tested in Chrome in Firefox). This behavior is defined in the W3C Content Security Policy spec:
Note: Modifications to the content attribute of a meta element after the element has been parsed will be ignored.
So is there any way to dynamically add (and more importantly also remove) a content security policy that does not rely on a HTTP navigation? I would like to avoid setting a restrictive image policy by default and then excepting individual images through hashes or nonces as this would be quite elaborate to implement.
In SPA you can each time to create a new fullscreen iframe and fill it by script. <iframe>, as nested browsing context, can have own CSP meta tag regardless of the parent page.
The parent page will contains only script to manage iframe's content, may be it's possible to use Worker() for this purpose.
I am getting the below error while running the application
Refused to apply inline style because it violates the following Content Security Policy directive: "style-src 'self' https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/ 'sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=' 'sha256-5uIP+HBVRu0WW8ep6d6+YVfhgkl0AcIabZrBS5JJAzs='". Either the 'unsafe-inline' keyword, a hash ('sha256-4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ='), or a nonce ('nonce-...') is required to enable inline execution.
Below is the code currently I am using
const string modernizrHash1 = "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=";
const string modernizrHash2 = "sha256-5uIP+HBVRu0WW8ep6d6+YVfhgkl0AcIabZrBS5JJAzs=";
app.UseCsp(options => options
.DefaultSources(s => s.Self())
.ScriptSources(s => s.Self().CustomSources("https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/"))
.StyleSources(s => s.Self().CustomSources("https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/", modernizrHash1, modernizrHash2))
.FontSources(s => s.Self().CustomSources("https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/fonts/"))
.ImageSources(s => s.Self().CustomSources("data:"))
);
The hash 4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ= is for the CSS word-wrap: break-word; white-space: pre-wrap;, the inline style Chrome automatically applies when you are not serving a HTML document;
Example server response:
Content-Type: text/plain; charset=utf-8
Content-Length: 9
Content-Security-Policy: default-src 'self'
Date: Thu, 04 Nov 2021 11:33:49 GMT
some text
DOM in Chrome
<html><head></head><body><pre style="word-wrap: break-word; white-space: pre-wrap;">some text</pre></body></html>
Console error
Refused to apply inline style because it violates the following Content Security Policy directive: "default-src 'self'"
. Either the 'unsafe-inline' keyword, a hash ('sha256-4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ='), or a nonce ('nonce-...') is required to enable inline execution. Note that hashes do not apply to event handlers, style attributes and javascript: navigations unless the 'unsafe-hashes' keyword is present. Note also that 'style-src' was not explicitly set, so 'default-src' is used as a fallback.```
Adding the hash to default-src or style-src won't help because it is an "inline style" and "hashes do not apply to style attributes".
The best fix is to make sure you serve a proper HTML document with your CSP header, so browsers don't decorate it with their own styling.
You are getting this error because the inline styles (which can be hashed to sha256-4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ=) aren't allowed, as per your Content Security Policy and the error that is returned.
I would recommend two possible steps, either:
Move away from inline styles (as they can be insecure) and will require you to change your CSP each time that the inline styles change.
Add the supplied SHA to the StyleSources for your CSP. But Be aware that this will have to be maintained and updated for each inline style added across all pages in your application.
UPDATE based on comments below answer
Note: There is no issue when i am running it in IE browser, only in the chrome and firefox i am getting the issue
Taking a look at Can I Use shows that IE has only partial support for Content Security Policy, which would explain why you aren't seeing this error in the console. i.e. Internet Explorer doesn't support CSP, so it isn't applying it.
I have fixed the issue by changing the hash keys shown in the browsers console error, I have replaced the console error hash key with my code hash key, but not sure whether this is the permanent solution or not
This is not really a permanent solution. If (and when) your inline styles change, you will have to change the hash in your CSP in order for the styles to be applied again.
Which leads me on to:
Could you please guide me how the hash keys are getting generated and how i can fix this permanently
Looking at the code in your original question:
const string modernizrHash1 = "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=";
const string modernizrHash2 = "sha256-5uIP+HBVRu0WW8ep6d6+YVfhgkl0AcIabZrBS5JJAzs=";
// other things
.StyleSources(s => s.Self().CustomSources("https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/", modernizrHash1, modernizrHash2))
You are telling the browser (via the Content Security Policy that you are generating) that it is only permitted to load styles from:
self (the origin domain of your site)
https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/
and those which match the following hashes:
sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=
sha256-5uIP+HBVRu0WW8ep6d6+YVfhgkl0AcIabZrBS5JJAzs=
You mention that you've also included the hash:
sha256-4Su6mBWzEIFnH4pAGMOuaeBrstwJN4Z3pq/s1Kn4/KQ=
When the browser starts to render the page, it will look at the resources that the page requires in order to render and will compare it to the list in the Content Security Policy. If a resource (inline styles and inline javascript are classed as a resource) is not in the list, then the browser will do a simple SHA-2 of the contents of the resource and compares it to any of the hashes listed in the CSP.
Note: the same thing can be achieved by the use of a nonce
If the resource isn't from an allowed source, or it's hash does not match those listed in the CSP, then the browser will actively refuse it.
Because the SHA-2 algorithm uses the content of the resource to generate the hash, when the contents of it changes the calculated value of the hash will be different.
For example, the inline style here:
<p style="color: red;">hello, world</p>
might hash to F1FF77E5DDBB1AF52EB51C98F725927143221549385937595112128987CF39E4 (which is the hash of "color:red")
whereas the following inline style:
<p style="color: green;">hello, world</p>
might has to 2F262B22412B633D12B27FA9F94A3B0495821CB8341CFF0A88C80E3FED5DC9E8 (which is the hash of "color:green")
As you can see, there is a massive difference in the hashed styles. This is by design (in the algorithm).
To stop alleviate this problem, I would swap the inline styles for a css file describing how the content of the page should be styled. As long as the css file is served from the same origin as your HTML, then the self rule will cover it.
CSP is a pretty complex topic to pick up (but easy to master, once you have learned the basics). I would recommend taking a look at the MDN page for Content Security Policy for more information on how it works and how you can use it to secure your web applications.
Summary:
Site at https://localhost:3000 , with Content-Security-Policy value of default-src 'self' 'unsafe-inline' https://localhost:3001/https_index.html contains iframe pointing at https://localhost:3001/index.html. The contents of :3001/index.html contain an . Clicking that link fails: Refused to frame '' because it violates the following Content Security Policy directive.... How can I change my CSP value to prevent this error; to open an new email in user's preferred email client (normal behavior of mailto)? I am using Chrome1
Detail:
Similar but different than this question "mailto link not working within a frame chrome (over https)
"
I think mine is not a duplicate because:
I cannot reproduce that bug, I see a console warning about mixed-content when I try to reproduce their steps:
Mixed Content: The page at 'https://localhost:3001/https_index.html' was loaded over HTTPS, but requested an insecure resource 'mailto:...'. This content should also be served over HTTPS.
My steps are specific; both my page & its iframe src are https, but the page itself is served with a specific and restrictive Content-Security-Policy (CSP):
app.use(csp({
directives: {
defaultSrc: ["'self' 'unsafe-inline' https://localhost:3001/https_index.html"]
}
}));
Also the resulting error I can reproduce is different:
Refused to frame '' because it violates the following Content Security Policy directive: "default-src 'self' https://localhost:3001/https_index.html". Note that 'frame-src' was not explicitly set, so 'default-src' is used as a fallback.
With an image like:
The accepted answers for the original questions will help me work around my CSP-specific issue, that is, if I add a target="_top" to the link, the email client opens without error:
<a target="_top" href="mailto:...">email</a>
A similar fix works for another similar but different issue. However, this may1 sometimes open a new tab
So my question is specifically about the Content-Security-Policy error (see above):
...Refused to frame '' because it violates the following Content Security Policy directive: ...
Notice it says frame ''. The frame is identified as an empty string!
Normally if some resource violates CSP, the URL of the resource is identified; i.e.
Refused to laod the script 'http://evil.com/evil.js'...
And if the CSP-violating URL is identified + provided I can use it; add it to my CSP value for default-src:
`app.use(csp({
directives: {
defaultSrc: ["http://evil.com/evil.js 'self' 'unsafe-inline' https://localhost:3001/https_index.html"]
}
}));`
But can I allow an exception for an href value? Specifically for mailto? I tried wildcards like mailto*, but:
The source list for Content Security Policy directive 'default-src' contains an invalid source: 'mailto*'.
And I wonder if any wildcard would work anyway; does Chrome really consider the href="mailto..." frame as an empty string? I suppose so, since it's not a URL per se; Chrome "wants" to launch an external application (i.e. Outlook) in the context of the iframe; who is bound to the CSP rules of its parent page...
Footnotes:
Chrome displays the above errors in CSP or sandbox cases. Internet Explorer doesn't complain about an iframes href, despite the value of CSP. Internet Explorer also doesn't have the "new tab" problem, despite the value of sandbox. IE 11.1914 will just give message:
The fix of using target="_top" may open a new tab , if you've sandboxed your iframe! (sandbox is different than CSP). I don't like the new tab. Chrome gave me this error...
Unsafe JavaScript attempt to initiate navigation for frame with URL 'http://localhost:3000/' from frame with URL 'https://localhost:3001/index.html'. The frame attempting navigation of the top-level window is sandboxed, but the flag of 'allow-top-navigation' or 'allow-top-navigation-by-user-activation' is not set.
... but opened a new tab, as well as the Outlook email client...
I did what the error suggested; modifying the value of the iframe sandbox attribute:
sandbox="allow-top-navigation allow-same-origin ...", and the mailto link worked (as before), but did not open an excessive new tab. Great!
Stumbled upon this question after encountering the same issue. There is surprisingly little documentation about this after hours of searching.
My first instinct was to do something like you were doing, mailto* or mailto:*.
What finally ended up working was omitting the wildcards, and altering the frame-src directive as such:
frame-src 'self' mailto: tel: *.mydomain.com
tel: links were also were broken in iframes.
I am embedding an iFrame in my web page, something like this:
var iframeProps = {
'data-type': self.props.type,
allowTransparency: self.props.allowTransparency,
className: self.props.className,
frameBorder: self.props.frameBorder,
height: self.props.height,
key: url,
onLoad: self.props.onLoad.bind(self),
scrolling: self.props.scrolling,
src: self.state.isActive ? url : '',
style: self.props.styles,
width: self.props.width
};
<iframe {...iframeProps} />
This is throwing an error in the console
Refused to display 'https://twitter.com/.... in a frame because an ancestor violates the following Content Security Policy directive: "frame-ancestors 'self'".
Could anyone please tell me how can I make this work?
The content is prohibited from being displayed within an IFRAME due the Content Security Policy being set. The webserver hosting twitter.com is configured to add a HTTP header to the response object. Specifically they are setting the Content-Security-Policy tag to frame-ancestors 'self'. There is no way you'll be able to embed their pages into a page of your own using IFRAME. There are other techniques that you could use to work around that, but none are as simple as an iframe tag.
W3C Content Security Policy Level 3 - Frame Ancestors
I encountered with this problems recently too and i didn't find any alternative method to solve that.Finally, I came up with idea that the attribute in the iframe,which is "src",can be filled with the origin html content and it works.
// this demo shows the process of getting the html content
// from the link,and then apply it to the attribute "src" in the iframe
$.get(link, function (response){
var html = response;
var html_src = 'data:text/html;charset=utf-8,' + html;
$("#iframeId").attr("src" , html_src);
});
This issue was occurring when trying to upload proof of identity documents to Amazon Pay. The solution was to clear the browser cache and cookies.